Actually, in the Star Trek and Mass Effect universes, aliens (and even many humans) don't speak English; communication is facilitated via advanced software that provides real-time translation. The Mass Effect games even mention that species & planets must update their language packs frequently as new words & expressions constantly enter languages.

Compare and contrast to the Star Wars and Lord of the Rings universes, where most everyone speaks a common language due to prolonged periods (dozens of millenia in the case of Star Wars) of inter-species or inter-stellar trade.

Adding a couple of things: The UT doesn't always work - or there are languages too complex for it to translate. This is shown many times in ST. In the series Enterprise, Hoshi Sato is the communications savant that developed it for Starfleet.

All that said, scientists today are working on a real life UT. The hardest part is the voice recognition software piece still being underdeveloped. There are just too many dialects and one needs to program all of it or an AI that can decipher tomato from tomahto. Pretty cool stuff tho and I DO want one!

Cheap, not very special effects. Back in the day, and even now, it's way cheaper to put a dude in a costume or makeup and say he's an alien than have formless masse or energy, creates that resemble flames or giant talking crab/monkey/budgie creatures in a TV show or movie, unless, it's a cartoon, as pointed out in other comments.

Yeah but nowadays we do have cheap off the shelf CGI effects. Imagination is the only limit when it comes to visual effects. The tiger in the season premier of Walking Dead was all done in CGI. Surely it can be used to do some truly alien forms.